PALEOTECTONIC AND PALEOGEOGRAPHIC CONDITIONS FOR THE ACCUMULATION OF THE LOWER RIPHEAN AI FORMATION IN THE BASHKIR UPLIFT (SOUTHERN URALS): THE TERRANECHRONE¯ DETRITAL ZIRCON STUDY

Romanyuk, T.V.; Kuznetsov, N.B.; Belousova, E.A.; Gorozhanin, V.M.; Gorozhanina, E.N.

Авторы: Romanyuk T.V., Kuznetsov N.B., Belousova E.A., Gorozhanin V.M., Gorozhanina E.N.
Журнал: Geodynamics & Tectonophysics
Том: 9
Номер: 1
Год издания: 2018
Издательство: Федеральное государственное бюджетное учреждение науки Институт земной коры Сибирского отделения РАН
Местоположение издательства: Иркутск
Первая страница: 1
Последняя страница: 37
DOI: 10.5800/gt-2018-9-1-0335
Аннотация: The results of an integrated study of detrital zircons separated from sandstones of basal horizons of the stratotypical Riphean sequence in the Southern Urals (the Navysh and Chudin suites of the Ai Formation of the Burzyan Group, Bashkir Uplift) using the TerraneChrone® technique (LA-ICP-MS) are presented. The contents of trace-elements in detrital zircons indicate the small role of complexes of oceanic or marginal-marine genesis among the primary sources of zircon and are in better agreement with intra-continental rather than passive margin origin of the Riphean basin, whose basal levels are composed by Ai Formation. U-Pb ages of the studied zircons in both samples are generally similar: Paleoproterozoic zircons predominate (the dominant peaks are actually coincided - 2063 and 2055 Ma), and the Archean is represented only by a few grains. However the Hf isotopic features and the contents of trace-elements of these zircons show significant differences between the samples, indicating that the zircon sources for the studied sandstones were complexes of different geodynamic nature. The characteristics of studied zircons can be explained in the framework of the model for the formation of the Ai Formation within a rift structure, namely into the Navysh graben, the predecessor of the Kama-Belaya aulacogen in the inner Volga-Uralian part of the Paleoproterozoic supercontinent Columbia. At the initial stage of rifting, the coarse clastic rocks (the Navysh suite) had been accumulated within the Navysh graben. The rocks are the erosional products of the lower silicic acidity granitoid complexes composing walls of this graben. A specific "carbonatitic" complex containing zircons with ages of about 2.0, 2.5, 2.85 and 3.6 Ga, and with the participation of the Palaeoarchean crustal material in the substrate of their parent rocks also had been eroded. In the final stage of rifting, already at the initial stages of the development of the Kama-Belaya aulacogen (Chudin suite), erosion products from the paleo-aquifers occupying vast areas began to be transportated into the rift. The primary sources of clastics for Chudin suite were both granitoids of lower and normal silicic acidity. Also a specific "carbonatitic" complex containing juvenile zircons with an ages of about 2.05 Ga had been eroded. However, by that time, significant areas of the Archaean basement of the Volga-Uralia had probably been hidden with a proto-cover and had not been eroded, so the Archean detritus in the Chudin suite is poorly represented in comparison with the Navysh suite both in number and in age of detrital zircons. Until now, the Precambrian carbonatite rocks neither within Taratash complex, which forms the basement of the Navysh graben, nor in the southeastern part of the East-European Platform have been described, and the question of the source of these "carbonatite" zircons is open, but has the prospect of being resolved as more data concerning basement rocks will have been accumulated. Key words: Bashkir uplift, Lower Riphean, detrital zircons, "TeraneChrone®" technique, Navysh graben, Kama-Belaya aulacogen, carbonatites, supercontinent Columbia.
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PALEOTECTONIC AND PALEOGEOGRAPHIC CONDITIONS FOR THE ACCUMULATION OF THE LOWER RIPHEAN AI FORMATION IN THE BASHKIR UPLIFT (SOUTHERN URALS): THE TERRANECHRONE¯ DETRITAL ZIRCON STUDYстатья

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